Typically, a damascene process is used to form interconnects for semiconductor processing. First, a trench is formed in a dielectric film on a substrate. A barrier metal is deposited to prevent the copper which will form the interconnect from diffusing through the dielectric layer. Subsequently, chemical polishing is performed on the copper interconnect and other layers are formed above the copper interconnect.
In order to provide an electrical connection to the interconnect, a via is used. A via hole is made in the layers above the copper interconnect to expose the copper interconnect. The via hole will be filled with some metal to provide an electrical connection. However, the surface of the copper in the interconnect may be oxidized or contain impurities due primarily to the chemical polishing. As a result, sufficient electrical contact cannot be made to the copper interconnect.
Conventional systems, such as those used in aluminum interconnection technology, sputter the surface of the interconnect metal. Sputtering causes copper and impurity atoms to be ejected from the exposed surface of the copper interconnect. Although the sputtering process removes the impurities from the surface of the copper interconnect, the impurities and copper are redeposited on the sides of the via hole. Because copper diffuses readily, the copper can diffuse through the layers above the copper interconnect. This diffusion can contaminate any junctions formed on the substrate.
Accordingly, what is needed is a system and method for providing sufficient electrical connection to the copper interconnect without introducing copper impurities to the circuit. The present invention addresses such a need.